The invention relates to fluid filters for filtering fluid from a machine, including spin-on type oil filters for internal combustion engines and hydraulic equipment, and more particularly to a filter with an indicator indicating when it is time to clean or replace the filter.
Filters are used on equipment and engines to reduce operating costs by slowing down component wear. As filters remove particles from lubricating fluid, the pressure drop across the filter element or media increases, and, if left unattended, the filter plugs. The increased pressure drop reduces the flow of fluid to the equipment or engine. Depending on the type of filter, this can result in increased wear rates, decreased fuel efficiency, and catastrophic failure. Further, particle removal efficiency typically declines as the pressure drop rises. Thus, filters need to be cleaned or changed before plugging becomes significant. Typically, filters are serviced, i.e. cleaned or replaced, at regular intervals of time or distance.
Commonly owned U.S. Pat. No. 5,462,679, incorporated herein by reference, discloses an in-situ cleanable oil filter that can be reused over and over again. Nonetheless, cleaning becomes less efficient over time, and the filter may gradually become too restrictive for use. Due to variability in operating conditions, it is impossible to predict in advance when plugging will occur. As a result, users must replace filter elements earlier than necessary, or alternatively after they have plugged. In the former case, users pay the cost of unnecessary filter replacement. In the latter case, accelerated equipment wear occurs, and maintenance costs can be higher. Therefore, it is desirable to have a device that indicates the optimal time to replace the filter media element. For cleanable filters, such as in the '679 patent, the optimal time for media element replacement is when the pressure drop across the media element exceeds a certain critical level. Typically, this occurs at a lower pressure than the terminal pressure drop of disposable elements, and lower than the pressure drop required to activate the filter bypass valve in engine oil and hydraulic oil systems. Unlike disposable filters, the cleanable filter is still removing particles, and its restriction is not excessive when this level is reached, but subsequent cleaning may not allow the filter to be used for an entire filter service interval.
For conventional disposable filters, the media element must be replaced when the pressure drop becomes excessive. At this point, particle removal efficiency is reduced and continued usage will only result in further reductions in removal efficiency and equipment protection. Furthermore, the restriction is such that either the equipment's filter bypass valve will open (and particle removal will be drastically reduced), or the flow through the filter and to oil lubricated components will decrease. Thus, the filter must be replaced at this time. Although filter media elements are typically changed at regular intervals, it is desirable to have an indicator to tell operators to replace the filter under unusual conditions.
The present invention was developed for use, in the preferred embodiment, with in-situ cleanable filters, though the invention can be used with either cleanable or disposable filters to determine when the filter media element needs to be replaced. Devices using pressure change, i.e. .DELTA.P, sensors of various types are known in the prior art and indicate the need for disposable filter element replacement. Typically, such sensors are incorporated into the filter mounting head for spin-on type filters and become a permanent part of the equipment. For some freestanding cartridge type filters, such .DELTA.P sensors are mounted onto the housing with oil lines connecting sampling points upstream and downstream of the element to a gauge or sensor. Some cartridge type filters with canister or bowl style housings have centrally mounted devices utilizing multiple components, fittings and connectors to indicate pressure drop.
In the present invention, in the preferred embodiment, the sampling line and sampling points are integral parts of the bottom of the filter housing, which also has a mounting port for the sensor fitting. For in-situ cleanable filters, in one embodiment, the port and fitting are radially offset from the center of the housing in order to avoid interference with the function of the air inlet cleansing port of the filter used for backflushing. For disposable filters, such port and fitting can be either radially offset or centered with respect to the bottom of the housing. The internal end of such port allows the sensor access to the high pressure side of the filter media element for in-situ cleanable filters. For disposable filters, it can provide access to either the low or high pressure side. A channel drilled into the housing connects the mounting port to the low pressure side of the media element for in-situ cleanable filters. For disposable filters, it can provide access to either the high or low pressure side as needed to measure .DELTA.P.
In the preferred embodiment, the .DELTA.P sensor is mounted in a single hydraulic type fitting that threads directly into the bottom end of the housing. The .DELTA.P sensor is preferably a movable piston, though other types may be used, such as piezoresistive type. The high pressure end of the fitting is equipped with a porous media, such as sintered metal, to dampen the effects of pressure surges on the sensor. This reduces the incidence of false indications of element plugging that may result from cold starts or changing flow rates. The porous media is also a filter, protecting the .DELTA.P sensor and preventing dirty fluid from reaching the clean side of the main filter, and preventing hydraulic lock of the .DELTA.P sensor when a piston type is used, because there is no film formation between the piston and a plate or the like with a hole therethrough. A connector located at the other end of the fitting allows the electrical output from the sensor to be connected to a DC power supply, such as a battery, and an appropriate display or monitor device, such as a dashboard mounted light, or to the equipment's electronic control module. The electrical connector provides for easy removal of the attached wires during filter element changes and installation. Either the sensor itself or the display/monitor device are set such that excessive pressure drop alerts the user that the filter element needs to be changed.
An advantage of the invention is that it can be used with either in-situ cleanable filters or conventional disposable filters. For cleanable filters, the invention has an advantage over alternatives in that in the preferred embodiment it is located radially offcenter and does not interfere with the operation of the air inlet cleansing port. Further for cleanable filters, the invention provides early warning of the need to replace the media element. Users may respond by cleaning the element more frequently until the element is replaced without fear of damaging their equipment. The invention reduces the number of components required for installation relative to other designs because it is located at the bottom of the permanent filter housing, instead of the filter mounting head, and allows easy installation onto existing filter heads, for example when used in conjunction with filters and filter housings such as shown in commonly owned U.S. application Ser. Nos. 08/755,479, filed Nov. 22, 1996, and 08/755,497, filed Nov. 22, 1996, now U.S. Pat. No. 5,779,900, incorporated herein by reference. Since most components are contained within either the housing or the fitting, they are better protected than alternative systems. Further, problems associated with wiring and fittings damaged by use are minimized, whether the filter is cleanable or disposable. This also facilitates installation by either the end user or the factory. To the end user, the invention has an advantage in that filter life can be determined directly and accurately for both cleanable and disposable filters.